The halogenated compounds, such as fluoro alkane sulfonic acids, have wide applications as super acids.
The U.S. Pat. Nos. 7,683,209 and 7,897,807 provide a process for preparing hydrofluoroalkanesulfonic acid by reacting fluoro olefin with sulfite in an aqueous solution adjusted to about pH 4 to pH 12. The water is removed from the solution to get a solid which is treated with oleum. The hydrofluoroalkanesulfonic acid is distilled therefrom.
The Journal of Organic Chemistry, 2008, 73, 711-714 provides a process for the preparation of potassium 1,1,2,2-tetrafluoroethanesulfonate from tetrafluoroethylene in a buffered aqueous solution of potassium sulfite and bisulfite and then converted to 1,1,2,2-tetrafluoroethane sulfonic acid in 90% overall yield by distillation from oleum solution.
The GB Patent No. 0,579,897, U.S. Pat. No. 2,403,207 and Journal of Organic Chemistry, 1949, 14, 747-753 also provide process(s) for preparation of tetrafluoroethanesulfonic acid or its salt.
The above cited prior art processes for preparation of tetrafluoroethanesulphonic acid proceed through hydrolysis of tetrafluoroethanesulphonate salt using sulfuric acid or oleum. The present inventors have observed that since the boiling point of tetrafluoroethanesulfonic acid is in the range of 210°-211° C., the tetrafluoroethanesulphonic acid has a strong affinity to stay in the pool of sulfuric acid when subjected to hydrolysis using either sulfuric acid or oleum. Therefore, stringent reaction conditions like high temperature and vacuum is required to recover the acid from the hydrolysis mixture. Moreover, it is not possible to extract the entrapped acid from the pool completely. Furthermore, such process is not feasible at industrial scale due to high incurring cost by the use of exotic materials of construction such as Inconel, Monel to name a few. Additionally, the use of dilute sulfuric acid (30-35% concentration) for hydrolysis of alkali metal salt of tetrafluoroethanesulfonic acid has a drawback of repeated ethereal extractions.
Thus, there is need in the art for a simple, cost effective and commercially viable method to prepare tetrafluoroethanesulfonic acid which obviates the use of high boiling sulfuric acid and harsh reaction conditions.